In this issue, I have listed some more
basic principles of MRI imaging including terminology.
Tissue Signal Characteristics
In the chart below, you will find a
basic reference chart that details the signal intensities that
anatomical structures should have upon T1 and T2 weighted MRI
images.
Please Note: Depending upon your video card, the following colors may appear altered.
Contraindications
| Cardiac pacemakers | Pregnancy |
| Cerebral aneurysm clips | Joint prostheses |
| Metallic fragments in eye | Braces and dentures |
| Cochlear implants | Intrauterine devices |
| Some shrapnel | Diaphragms |
| Surgical staples wires | |
| Most penile implants |
Terminology:
Disc Protrusion
Bulge: The disc protrudes in a broad, non-focal way. This term describes a process that is degenerative in nature.
Protrusion: Outpouching of disc, may be focal or broad based.
Herniation: Focal protrusion of disc.
Prolapse: Herniated -- may be used to describe a disc herniation that is not contained by the outer most annulus fibrosus (OMA) nor the posterior longitudinal ligament (PLL).
Sequestration: A displaced fragment of disc within the canal.
Free fragment:
Same as sequestered disc.
Disc herniation
Contained: Nuclear material is contained by OMA and/or PLL.
Non-contained: Nuclear material not contained by the OMA nor the PLL.
Sequestrated: A displaced fragment of disc within the in canal.
Dissecting:
Herniated disc material that is coursing under PLL.
Location of herniation / protrusion
Central: Straight posterior.
Paracentral: Eccentric but posterior.
Lateral: Toward the medial aspect of the intervertebral foramen (IVF).
Foraminal: Extending into the IVF.
Far lateral: Lateral but at the anterior aspect of or anterior to the IVF.
Anterior:
Anterolateral:
Superior or Inferior: Disc material that herniated through the vertebral endplate (Schmorl's node)
Limbus vertebrae:
Schmorl's node that shears off a portion of the vertebral ring
apophysis, anterior or posterior.
Disc degeneration
Disc desiccation: Decreased signal within the disc on T2 weighted images. This is the earliest visible stage of disc degeneration. The disc is drying out.
Disc dehydration: See disc desiccation.
Internal derangement: This refers to a rent within the inner annular fibers of the disc and implies migration of the nucleus pulposus into the rent or tear.
Degenerative broad-based disc protrusion: A disc bulge.
Spinal stenosis:
The neural structures within the spinal canal (ex: cauda equina)
are impinged upon by the bony spinal canal or by a space occupying
mass within the canal.
Dr. Knudsen is a board certified chiropractic radiologist (D.A.C.B.R.) and is Director of Clinical Diagnostic Imaging at National College of Chiropractic in Lombard, Illinois. For more information about Dr Knudsen's radiology consulting services, MRI imaging, or quality control issues, please call Dr. Knudsen at (800)469-9729.